WO2026013169A2

WO2026013169A2 - Stabilization of polypropylene recycling material against degradation

Info

Publication number: WO2026013169A2
Application number: PCT/EP2025/069669
Authority: WO
Inventors: Alexandra Romina ALBUNIA; Yuliia ROMANENKO; Bernadette DUSCHER; Peter Denifl; Paul Baumann
Original assignee: Borealis GmbH
Current assignee: Borealis GmbH
Priority date: 2024-07-11
Filing date: 2025-07-10
Publication date: 2026-01-15
Anticipated expiration: 2027-01-11

Abstract

The present invention relates to a process for stabilizing a polypropylene recycling material against degradation, preferably oxidative and/or thermal degradation, as well as to compositions for the stabilization of a polypropylene recycling material.

Description

Stabilization of polypropylene recycling material against degradation

Field of the Invention

Background of the Invention

Polyolefins, in particular polyethylene and polypropylene, are increasingly consumed in large amounts in a wide range of applications, including packaging for food and other goods, fibers, automotive components, wires and cables, and a great variety of manufactured articles.

Considering the huge amount of waste collected compared to the amount of waste recycled back, there is still great potential for intelligent reuse of plastic waste and for mechanical recycling of plastic wastes.

Often, recycling materials of polyolefins on the market are mixtures of both polypropylene (PP) and polyethylene (PE), this is especially true for post-consumer recycling (PCR) waste. Moreover, post-consumer recycling waste is conventionally cross contaminated with nonpolyolefin materials, such as polyethylene terephthalate, polyamide, polystyrene or non- polymeric substances like wood, paper, glass or aluminum. These cross-contaminations drastically limit final applications of recycled polyolefins.

Recycled polyolefins normally have properties, which are deteriorated compared to those of virgin, i.e., freshly produced, polyolefins. For example, recycled polyolefins often have limited mechanical and optical properties and thus, they do not fulfil customer requirements. Journal of Polymers and the Environment 30, 494-503, (2022), discloses the change of melt flow rate of recycled polypropylene depending on the contaminant content and the recycling process. Further, a much shorter oxidation induction time and a much lower oxidation induction temperature are recorded for contaminated reprocessed polypropylenes.

Particularly due to the contaminants in recycling materials, already established additive compositions for virgin polymers are usually not sufficient to provide stabilization of recycling materials. Contaminations in the polyolefin recycling materials and processing of these materials can reduce or eliminate the effectiveness of certain additives. As the compositions of recycling materials are very inhomogeneous, the contents of contaminants vary to high extents. Thus, their effect on polymer degradation and other properties are complex and not easy to predict. Accordingly, additive packages generally used for virgin polymers may not be efficiently stabilizing. Moreover, stabilizing additives suggested for recycling polyethylene materials may not be suitable for recycling polypropylene materials and vice versa. Therefore, there is a need in the art for stabilizing methods for recycling polyolefin materials in order to prevent degradation thereof and to improve the properties of the recycled polyolefin products. These methods should be cost-efficient and integrable in common recycling processes.

Summary of the Invention

The present invention is based on intense studies of the contents of polypropylene recycling material, in particular polypropylene recycling material originating from packaging applications, e.g., from flexible material such as polypropylene films, and the evaluation of required additives for improving stability of the recycled products prepared thereof.

Accordingly, the present invention is directed to a process for stabilizing a polypropylene recycling material against degradation, comprising extrusion-blending a polypropylene recycling material with a) from 0.02 to 0.25 wt.-% of one or more primary antioxidant(s), b) from 0.02 to 0.28 wt.-% of one or more secondary antioxidant(s), c) from 0.05 to 0.60 wt.% of one or more metal deactivator(s), and d) from 0.00 to 5.00 wt.-% of further additive(s) and/or additive carrier(s), to form a stabilized polypropylene recycled product, wherein the polypropylene recycling material comprises, based on the total weight of the polypropylene recycling material, from 2 to less than 20,000 ppm of the sum of contents of the transition metals selected from titanium (Ti), zinc (Zn), copper (Cu) and iron (Fe), determined by X-ray fluorescence (XRF) spectroscopy as described herein.

The process according to the present invention enables stabilization of polypropylene recycling material with a wide range of different contaminants and reduces degradation, particularly oxidative and/or thermal degradation, of the final recycled product. The process according to the present invention is particularly suitable for the stabilization of polypropylene recycling material originating from packaging applications. Respective polypropylene recycling material is characterized by typical contents of specific metals (e.g., transition metals), which can be sufficiently bonded by the composition of additives incl. the one or more metal deactivators. For example, packaging materials typically have relatively low contents of copper and relatively high contents titanium.

The process according to the present invention can be easily integrated in established polypropylene recycling processes, and when using common additives from the selected classes of additives, the costs can be held relatively low. The present invention is also directed to the stabilized polypropylene recycled product obtainable by the process according to the present invention.

Further, the present invention is also directed to a composition for stabilizing a polypropylene recycling material against degradation, comprising a) one or more primary antioxidant(s), b) one or more secondary antioxidant(s), c) one or more metal deactivator(s), and d) optionally further additive(s) and/or additive carrier(s), wherein the polypropylene recycling material comprises, based on the total weight of the polypropylene recycling material, from 2 to less than 20,000 ppm of the sum of contents of the transition metals selected from titanium (Ti), zinc (Zn), copper (Cu) and iron (Fe), determined by X-ray fluorescence (XRF) spectroscopy as described herein.

Still further, the present invention is directed to the use of this composition for stabilizing said polypropylene recycling material against degradation.

Description of the Invention

Process

The present invention is directed to a process for stabilizing a polypropylene recycling material against degradation, preferably oxidative and/or thermal degradation.

Polypropylene recycling material

According to the present invention, the process employs a polypropylene recycling material as the material to be stabilized. As used herein, the wording “polypropylene recycling material" denotes a polypropylene material that has completed at least a first use cycle (or life cycle), i.e., has already served its first purpose. Usually, polypropylene recycling material originates from waste, such as consumer waste. In contrast, industrial waste is manufacturing scrap, which does normally not reach a consumer. Preferably, polypropylene recycling material originates from consumer waste, such as waste that may be obtained from conventional collecting systems, e.g., those implemented in the European Union.

Such post-consumer waste material (and thus also polypropylene recycling material) may e.g., be characterized by a limonene content of at least 0.1 ppm (determined by solid phase microextraction (HS-SPMEGC-MS) by standard addition), which is usually not present in virgin polymer material, i.e., a polymer material freshly prepared. Further, polypropylene recycling material often contains a mixture of different polypropylene polymers. Further, often other polyolefins and non-polyolefin polymers (e.g., polystyrene, polyethylene terephthalate, polyamide etc.) may be present in the polypropylene recycling material, since it originates from a mixture of polymeric articles. One single polymer article may be composed of only one single kind of polymer or already from different kinds of polymers. In addition to the different polymers, other components may be present in the polypropylene recycling material also originating from post-consumer waste, such as wood, paper, limonene, aldehydes, ketones, fatty acids, metals, and/or long-term decomposition products of stabilizers. These components are usually not contained in virgin polymer material.

As used herein, the wording “polypropylene” denotes a propylene homopolymer and propylene copolymer and combinations (e.g., blends) thereof. Propylene homopolymers generally comprise at least 98 wt.-%, based on the total weight of the homopolymer, of units derived from propylene. Propylene copolymers generally refer to polymers comprising more than 50 wt.-%, based on the total weight of the copolymer, of units derived from propylene and further units derived from other polymer monomers, particularly ethylene and/or alpha-olefin units having from 4 to 12 carbon atoms.

According to the invention, the polypropylene recycling material comprises at least 80 wt.-%, preferably at least 85 wt.-%, and more preferably at least 90 wt.-%, based on the total weight of the polypropylene recycling material, of polypropylene, i.e., propylene homopolymers, propylene copolymers and combinations (e.g., blends) thereof. Accordingly, nonpolypropylene polymers and other components (as described above for the post-consumer waste) may be present in the polyolefin in a content of less than 20 wt.-%. The polypropylene content may be in the range of from 80 to 99.7 wt.-%, preferably from 85 to 99.5 wt.-%, such as from 90 to 99 wt.-%.

If not indicated otherwise in this disclosure, “%” generally denotes weight percent.

Generally, the content of polymers and monomer units can be measured by spectroscopic methods, in particular, by Fourier-transform infrared (FTIR) spectroscopy.

The polypropylene recycling material used according to the present invention is preferably of sufficient purity to be used as final polypropylene recycled product for a variety of applications. It has been found that polypropylene recycling material with the below described properties is particularly suitable to be used in the process of the present invention, and excellent stabilization of such material can be reached by the process.

Preferably, the polypropylene recycling material has a sum of contents of contaminants selected from polyamide (PA), polyethylene terephthalate (PET) and polystyrene (PS) of less than 2.5 wt.-%, such as less than 2.3 wt.-%, based on the total weight of the polypropylene recycling material and determined by Fourier-transform infrared (FTIR) spectroscopy as described herein below. The sum of contents of these contaminants may be in the range of from 0.0 to less than 2.5 wt.-%, such as from 0.1 to less than 2.3 wt.-%.

According to the present invention, the polypropylene recycling material has a sum of contents of the transition metals selected from titanium (Ti), zinc (Zn), copper (Cu) and iron (Fe) of less than 20,000 ppm, preferably less than 18,000 ppm, such as less than 10,000 ppm, based on the total weight of the polypropylene recycling material and determined by X-ray fluorescence (XRF) spectroscopy as described herein below. The sum of contents of these contaminants ranges from 2 to less than 20,000 ppm, preferably from 5 to less than 18,000 ppm, such as from 10 to less than 10,000 ppm.

In some embodiments, the polypropylene recycling material has a sum of contents of the transition metals selected from zinc (Zn), copper (Cu) and iron (Fe) of less than 300 ppm, preferably less than 250 ppm, such as less than 100 ppm, based on the total weight of the polypropylene recycling material and determined by X-ray fluorescence (XRF) spectroscopy as described herein below. The sum of contents of these contaminants may be in the range of from 0 to less than 300 ppm, preferably from 0 to less than 250 ppm, such as from 1 to less than 100 ppm.

In some preferred embodiments, the polypropylene recycling material has a copper (Cu) content of less than 150 ppm, preferably less than 100 ppm, such as less than 50 ppm, based on the total weight of the polypropylene recycling material and determined by X-ray fluorescence (XRF) spectroscopy as described herein below. The copper content may be in the range of from 0 to less than 150 ppm, preferably from 0 to less than 100 ppm.

Preferably, the polypropylene recycling material comprises, based on the total weight of the polypropylene recycling material, a calcium (Ca) content of from 100 to less than 30,000 ppm, based on the total weight of the polypropylene recycling material and determined by X-ray fluorescence (XRF) spectroscopy as described herein below.

Preferably, the polypropylene recycling material comprises, based on the total weight of the polypropylene recycling material, an aluminum (Al) content of from 10 to 1 ,000 ppm, preferably from 20 to less than 800 ppm, based on the total weight of the polypropylene recycling material and determined by X-ray fluorescence (XRF) spectroscopy as described herein below.

In some embodiments, the polypropylene recycling material is characterized by at least one, preferably all of the following metal contents, based on the total weight of the polypropylene recycling material and determined by X-ray fluorescence (XRF) spectroscopy as described herein below: a) a content of calcium (Ca) of less than 30,000 ppm, preferably less than 20,000 ppm, such as in the range of from 100 to less than 30,000 ppm; b) a content of titanium (Ti) of less than 20,000 ppm, preferably less than 16,000 ppm, such as in the range of from 50 to less than 20,000 ppm; c) a content of iron (Fe) of less than 400 ppm, preferably less than 300 ppm, such as less than 150 ppm or in the range of from 2 to less than 400 ppm; d) a content of zinc (Zn) of less than 150 ppm, preferably less than 100 ppm, such as in the range of from 2 to less than 150 ppm; and e) a content of copper (Cu) of less than 150 ppm, preferably less than 100 ppm, such as in the range of from 1 to less than 150 ppm.

Preferably, in some embodiments (more preferably, in the above embodiments), the polypropylene recycling material is further characterized by a content of aluminum (Al) of less than 1 ,000 ppm, preferably less than 800 ppm, such as in the range of from 10 to less than 1 ,000 ppm.

The polypropylene recycling material used according to the present invention is preferably characterized by the properties described in the following. It has been found that polypropylene recycling material with the below described properties is particularly suitable to be used in the process of the present invention.

Preferably, the polypropylene recycling material has from 1 to 15 wt.-% of ethylene units (C2), based on the total weight of the polypropylene recycling material and determined by Fourier- transform infrared (FTIR) spectroscopy as described herein below.

Preferably, the polypropylene recycling material has a melt flow rate MFR2 in the range of from 3 to 12 g/10 min, preferably from 4 to 10 g/10 min, such as from 5 to 9 g/10 min, determined according to ISO 1133, 230 °C, 2.16 kg.

Preferably, the polypropylene recycling material is characterized by at least one, more preferably all, of the following properties, determined by CRYSTEX QC analysis as described herein below: i) an intrinsic viscosity (IV) in the range of from 1.5 to 2.2 dl/g, such as from 1.6 to 2.1 dl/g; ii) an ethylene content (C2) in the range of from 2.0 to 10.0 wt.-%, preferably from 2.5 to 9.0 wt.-%, relative to the total weight of the polypropylene recycling material; iii) a content of soluble fraction (SF) in the range of from 3.0 to 15.0 wt.-%, preferably from 3.5 to 13.0 wt.-%, more preferably from 4.0 to 11.0 wt.-%, relative to the total weight of the polypropylene recycling material; iv) an intrinsic viscosity (IV(SF)) of the soluble fraction (SF) in the range of from 0.5 to 2.0 dl/g, such as from 0.6 to 1 .9 dl/g; v) an ethylene content (C2(SF)) of the soluble fraction (SF) in the range of from 5.0 to 35.0 wt.-%, preferably from 6.0 to 30.0 wt.-%, relative to the total weight of the soluble fraction (SF); vi) a content of the crystalline fraction (CF) in the range of from 85.0 to 97.0 wt.-%, preferably from 87.0 to 96.5 wt.-%, relative to the total weight of the polypropylene recycling material; vii) an intrinsic viscosity (I V(CF)) of the crystalline fraction (CF) in the range of from 1.5 to 2.2 dl/g, such as from 1.6 to 2.1 dl/g; and viii) an ethylene content (C2(CF)) of the crystalline fraction (CF) in the range of from 1 .5 to 10.0 wt.-%, preferably from 2.0 to 8.0 wt.-%, relative to the total weight of the crystalline fraction (CF).

The polypropylene recycling material can be employed in the process in the form obtained from a provider (e.g., a waste collection system) if it already has the required polypropylene content and preferably other properties (e.g., sufficient purity) to be used as a recycled product. It may also be presorted to obtain a concentrated content of polypropylene material.

It is particularly preferred that the polypropylene recycling material originates from packaging polypropylene recycling material, particularly from flexible polypropylene recycling articles. The wording “flexible polymer articles" or “flexible polymer material" (such as flexible polypropylene recycling articles/material) is well known in the art of polymer technology and is contrasted to the wording “rigid polymer articles" or “rigid polymer material" . For example, a distinction may be made based on the thickness of these articles or material, i.e. , typically, flexible polymer articles/material are objects that are thinner than 120 pm. The thickness can be measured on a sample of flexible polymer articles/material by a micrometer gauge. Usually, flexible polymer articles/material are objects made from thin continuous plastic materials, i.e., plastic films, fibers, and all plastic fabrics (e.g., woven and melt-blown fibers). Preferably, the flexible polypropylene recycling material comprises objects, wherein at least 70 wt.-% of the objects are of flexible material, i.e., are thinner than 120 pm.

Often, it may be required that the polypropylene recycling material is prepared by mechanical recycling from a precursor polyolefin recycling material, which does not have the required polypropylene content and/or purity. A suitable mechanical recycling process for the preparation of the polypropylene recycling material to be used in the process according to the present invention may comprise any, preferably all, of the following steps: a) providing a precursor polyolefin recycling material stream (A) that contains polypropylene recycling material, preferably flexible polypropylene recycling material; b) sieving the precursor polyolefin recycling stream (A) to create a sieved polyolefin recycling stream (B) having only articles with a longest dimension in the range of from 30 to 400 mm; c) removing metal articles from the sieved polyolefin recycling material stream (B) to obtain a purer polyolefin recycling stream (C); d) sorting the polyolefin recycling material stream (C) by means of one or more optical sorters at least by polymer type, transparency and color, and optionally reflectance, and selecting the polypropylene colored or polypropylene transparent fraction, thereby generating a sorted polypropylene recycling material stream (D); e) reducing the size of the sorted polypropylene recycling stream (D) to form a flaked polypropylene recycling material stream (E); f) washing the flaked polypropylene recycling material stream (E) in an alkaline solution at a temperature in the range of from 20 to 95 °C to obtain a washed polypropylene recycling material stream (F); g) drying the washed polypropylene recycling stream (F) to obtain a dried polypropylene recycling material stream (G); and h) optionally conducting further recycling steps, such as separating flexible material from rigid material and/or a pre-extrusion without additive addition and/or aeration, on the dried polypropylene recycling material stream (G), to obtain a further processed polypropylene recycling material stream (H).

The specific steps of the mechanical recycling are inter alia described in WO 2023/118421 A1 , WO 2023/180222 A 1 and WO 2023/209075 A1. It is referred to these documents for more details.

Any of the polypropylene recycling material streams (G) and (H) represent suitable material for stabilization for the process according to the present invention.

The process preferably comprises additional steps of controlling the quality obtained after one or more of the above-described steps, such as after the sorting step d) and/or directly before an optional pre-extrusion step h) or before the extrusion-blending of the process according to the present invention. Such steps are generally carried out on a sample drawn from the polymer stream. Generally, the polypropylene recycling material may be in a (physical) form suitable for the extrusion-blending. For example, the polypropylene recycling material may be in the form of flakes obtained by a size-reducing, e.g., shredding step. Suitable flakes preferably have a surface area in the range of from 50 to 2500 mm², more preferably from 100 to 1600 mm² and most preferably from 150 to 900 mm². In the context of the present description, the flake surface area is defined as the surface area of one of the faces of a flake. This surface area is approximately half of the total surface area of the flake, which has two such faces in addition to a very small amount of surface area coming from the edges of the flake. Accordingly, the total surface area of the flake can range to more than 5000 mm².

It is also possible that the polypropylene recycling material is already present as a preextruded material, i.e., it has passed an extrusion step without addition of any additives. Dosing of additives is facilitated if the polypropylene recycling material is in a pre-extruded form.

Process steps

The process according to the present invention comprises extrusion-blending a polypropylene recycling material with specific additives. This means that the polypropylene recycling material is blended, i.e., mixed, with specific additives during an extrusion step.

Usually, the polypropylene recycling material is placed in an extrusion device and the additives are added. Generally, the additives may be added to the polypropylene recycling material as single components, as compositions of some of these additives or as a composition of all additives (i.e., “onepack”), possibly further comprising a carrier (e.g., in the form of a masterbatch). The compositions are further described herein below.

The extrusion step may be carried out by a conventional compounding or blending apparatus or an extruder, e.g., a single or a twin-screw extruder, such as a co-rotating twin-screw extruder.

It is preferred that the extrusion is a melt-extrusion and it preferably includes a melt- filtration step, wherein larger gels and other particles are reduced in size by filtration. This notably reduces the content of respective inclusions of larger sizes (such as >50 pm) and improves the quality of the polypropylene recycled product.

The melt- filtration step may include one or more filtration sub-steps, which may optionally be separated by a degassing and/or vacuumizing sub-steps. Generally, in the filtration sub- step(s), filters may be employed such as in the form of filter discs (preferably continuous laser filter discs). In case of more than one filtration sub-step, the average pore sizes of the filters may be the same or different. Preferably, the average pore sizes of the filters decrease with the sequence of the filtration sub-steps. This enables efficient filtration with less contamination and blocking of the filters, as the particles are separated by the filters in the sequence of reduced sizes.

The first filter may comprise a perforated metal plate or drum, and the second filter may comprise a fiber mesh, for example, a metal fiber mesh. The second filter may be a screen changer or a belt filter. The first filter may have a mesh size of 70 to 150 pm, preferably 75 to 130 pm, more preferably 80 to 110 pm. The second filter may have a mesh size of 40 to 130 pm, preferably 45 to 110 pm, more preferably 50 to 100 pm. The second filter may have a mesh size smaller than that of the first filter. Perforations in the first filter may be formed by laser (laser filter).

A cascade of filters may be used, for example, a cascade of more than two filters is used, such as three, four or five filters. Where a cascade of two or more filters is used, the second or subsequent filter may have a mesh size that is smaller than the mesh size of the filter that immediately precedes it in the cascade.

The first filter may have perforations that are not uniform in cross-section. For example, the perforations may be frustoconical in cross section, such that each perforation has a minor and major diameter. The second filter may have a mesh size that is smaller than at least the major diameter of the first filter, preferably smaller than both the major and minor diameter of the first filter.

The process according to the present invention may also comprise the above-discussed steps of mechanical recycling as integral parts of the process. Accordingly, in some embodiments, the process according to the present invention comprises the steps a) to h) as described above, and further comprises: i) extrusion-blending the polypropylene recycling material stream (G) or (H) with one or more primary antioxidant(s), one or more secondary antioxidant(s), one or more metal deactivator(s), and optionally further additives and/or additive carriers, to form a stabilized polypropylene recycled product (I); j) preferably pelletizing, the stabilized polypropylene recycled product (I) to form a pelletized stabilized polypropylene recycled product (J); and k) optionally aerating the stabilized polypropylene recycled product (I) or (J) to remove volatile organic compounds, thereby generating an aerated, preferably pelletized, stabilized polypropylene recycled product (K). Stabilized polypropylene recycled product

By the process according to the present invention, a stabilized polypropylene recycled product is formed.

As used herein, a “recycled’ polymer material or product (e.g., recycled polypropylene product) denotes a polymer material that has been prepared from a respective polymer recycling material by a recycling process and can be used in the general application of polymers. Usually, polymer recycled product is prepared from polymer recycling materials by purification (and optional pre-extrusion without additive addition) and subsequent extrusion in the presence of additives.

Generally, the stabilized polypropylene recycled product is characterized by a very similar content of polymers and metals as described above for the polypropylene recycling material. Thus, the above-described ranges are the same for the stabilized polypropylene recycled product. However, in addition, the stabilized polypropylene recycled product comprises the additives added as well as degradation products (of additives) which occur during the blendextrusion.

The stabilized polypropylene recycled product is stabilized against degradation, preferably oxidative and/or thermal degradation. Accordingly, the degradation of the stabilized polypropylene recycled product is decelerated and/or minimized. This can be seen in the change of the oxidation induction time (OIT) at 200 °C and enhanced temperature of the oxidation induction, as well as on the lower contents of other typical polypropylene degradation products (e.g., acetic acid etc.) and/or volatile compounds.

Additives

In the process according to the present invention, a polypropylene recycling material is extrusion-blended with a) from 0.02 to 0.25 wt.-% of one or more primary antioxidant(s), b) from 0.02 to 0.28 wt.-% of one or more secondary antioxidant(s), c) from 0.05 to 0.60 wt.% of one or more metal deactivator(s), and d) from 0.00 to 5.00 wt.-% of further additive(s) and/or additive carrier(s).

Virtually all polymeric materials undergo oxidation and degradation reactions. Oxidation can occur at every stage of the life cycle of a polymer, i.e. , during manufacturing and storage of the material or during processing and end-use. Typical manifestations of oxidation of polymers can be change of viscosity during processing, appearance, and loss of mechanical properties such as elongation, impact strength, tensile strength, and flexibility. It is generally known that antioxidants protect polymers against oxidation by controlling molecular weight changes that lead to a loss of physical, mechanical, and optical properties.

Among other factors heat, light and mechanical stress can result in degradation of polymers. Antioxidants interrupt the degradation processes in different ways depending on their structures.

Generally, antioxidants are divided into three main groups: primary antioxidants, secondary antioxidants and alkyl radical scavengers. Sometimes (alkyl) radical scavengers are allocated to the group of primary antioxidants. Within the disclosure of the present invention, alkyl radical scavengers are considered as a third group of antioxidants, in addition to the primary antioxidants and secondary antioxidants. a) Primary antioxidants

Primary antioxidants are known to prevent polymer degradation by trapping free radicals. In a typical reaction, primary antioxidants donate hydrogen to the peroxy (ROO*), hydroxy (*OH) or alkoxy (RO*) radicals that transfer them into inert species. A typical reaction with a primary antioxidant (a phenolic antioxidant) is depicted in the following (simplified) scheme:

Scheme 1 : Mechanism of peroxy radical quenching with a phenolic primary antioxidant.

It has been found that primary antioxidants are effective during both polymer processing and long-term ageing. Hindered phenols and aromatic amins are typical commercial examples of primary antioxidants.

Preferably, the one or more primary antioxidant(s) comprise(s) a phenolic antioxidant. It has been found that phenolic antioxidants provide less discoloration of the polymer than aromatic amine antioxidants. Thus, phenolic antioxidants are particularly useful for light-colored polymers, for example for polymers obtained from transparent fractions of polyolefin recycling material.

The one or more primary antioxidant(s) is/are preferably selected from the group consisting of 2,6-di-tert-butyl-4-methyl phenol, pentaerythrityl-tetrakis(3-(3’,5’-di-tert-butyl-4- hydroxyphenyl)propionate, octadecyl 3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate, 1 ,3,5- tri-methyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxyphenyl)benzene, 2,2’-thiodiethylenebis-(3,5-di- tert-butyl-4-hydroxyphenyl)propionate, calcium (3,5-di-tert-butyl-4-hydroxy benzyl monoethyl- phosphonate), 1 ,3,5-tris(3’,5’-di-tert-butyl-4’-hydroxybenzyl)-isocyanurate, bis-(3,3-bis-(4’- hydroxy-3’-tert-butylphenyl)butyric acid)glycolester, 4,4’-thiobis(2-tert-butyl-5-methylphenol), 2,5,7,8-tetramethyl-2(4’,8’,12’-trimethyltridecyl)chroman-6-ol, 1 ,3,5-tris(4-tert-butyl-3- hydroxy-2,6-dimethylbenzyl)-1 ,3,5-triazine-2,4,6-(1 H,3H,5H)-trione, 4,6-bis (octylthiomethyl)- o-cresol, butylated reaction product of p-cresol and dicyclopentadiene, and any combination thereof.

These (hindered) phenols act as H donors to convert peroxyl radicals into stable peroxides at room temperature. As a result of this reaction, phenolic antioxidant is converted into phenoxy radicals (PhO) (Scheme 1).

It has been empirically found that some primary antioxidants are particularly suitable for stabilization of polypropylene recycling material, and the one or more primary antioxidant(s) is/are more preferably selected from the group consisting of pentaerythrityl-tetrakis(3-(3’,5’-di- tert-butyl-4-hydroxyphenyl)propionate (e.g., Irganox 1010®, BASF), 1 ,3,5-tri-methyl-2,4,6-tris- (3,5-di-tert-butyl-4-hydroxyphenyl)benzene (e.g., Irganox 1330 FF®, BASF), 2, 5,7,8- tetramethyl-2(4’,8’,12’-trimethyltridecyl)chroman-6-ol (e.g., Irganox E201®, BASF) and any combination thereof. The most preferred antioxidant is pentaerythrityl-tetrakis(3-(3’,5’-di-tert- butyl-4-hydroxyphenyl)propionate (e.g., Irganox 1010®, BASF).

According to the present invention, the polypropylene recycling material is extrusion-blended, based on the total weight of the stabilized polypropylene recycled product, with from 0.02 to 0.25 wt.-%, preferably from 0.03 to 0.15 wt.-%, more preferably from 0.03 to 0.12 wt.-%, such as from 0.04 to 0.08 wt.-%, of the one or more primary antioxidant(s).

The polypropylene recycling material is preferably extrusion-blended with one to three, more preferably with one or two and most preferably with one primary antioxidant, wherein the primary antioxidants are preferably selected from the compounds depicted above. b) Secondary antioxidants

Secondary antioxidants are known to act as hydroperoxide decomposer. Basically, they decompose hydroperoxides into non-reactive products before they start decomposing with formation of alkoxy and hydroxy radicals. Secondary antioxidants do not react with radicals. A typical reaction with a secondary antioxidant (a phosphite antioxidant) is depicted in the following scheme: Scheme 2: Main mechanism of peroxide decomposition by a phosphite secondary antioxidant.

Typical secondary antioxidants are organic phosphorous compounds (e.g., phosphites and phosphonites) and thioethers.

The one or more secondary antioxidant(s) is/are preferably selected from the group consisting of tris(2,4-di-tert-butylphenyl)phosphite, tetrakis-(2,4-di-tert-butylphenyl)-4,4’-biphenylen-di- phosphonite, di-stearyl-pentaerythrityl-di-phosphite, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, 2-(1 ,1-dimethylethyl)-6-methyl-4-[3-[[2, 4,8,10-tetrakis(1 , 1 -dimethylethyl)di- benzo[d,f][1 ,3,2]dioxaphosphepin-6-yl]oxy]propyl]phenol, di-stearyl-thio-di-propionate, di- lauryl-thio-di-propionate, di-octadecyl-disulfide, and any combination thereof.

More preferably, the one or more secondary antioxidant(s) is/are organic phosphorous secondary antioxidant(s), preferably selected from the group consisting of tris(2,4-di-tert- butylphenyl)phosphite, tetrakis-(2,4-di-tert-butylphenyl)-4,4’-biphenylen-di-phosphonite, di- stearyl-pentaerythrityl-di-phosphite, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, 2-(1 , 1- dimethylethyl)-6-methyl-4-[3-[[2,4,8,10-tetrakis(1 ,1-dimethylethyl)di- benzo[d,f][1 ,3,2]dioxaphosphepin-6-yl]oxy]propyl]phenol, and any combination thereof. It has been found that organic phosphorous secondary antioxidants are particularly suitable for stabilization of polypropylene recycling material which is then used as recycled products in film applications. The organic phosphorous secondary antioxidants are most effective during processing and protect both the polymer and the primary antioxidant.

Even more preferably, the one or more secondary antioxidant(s) is/are organic phosphorous secondary antioxidant(s), selected from the group of consisting of tris(2,4-di-tert- butylphenyl)phosphite (e.g., Irgafos 168 (FF)®, BASF), bis(2,4-dicumylphenyl)pentaerythritol diphosphite (e.g., Doverphos S-9228 CT®, Dover Chemical), 2-(1 ,1-dimethylethyl)-6-methyl- 4-[3-[[2,4,8,10-tetrakis(1 ,1-dimethylethyl)di-benzo[d,f][1 ,3,2]dioxaphosphepin-6- yl]oxy]propyl]phenol (e.g., Sumilizer GP®, Sumitomo Chemical) and any combination thereof; with tris(2,4-di-tert-butylphenyl)phosphite (e.g., Irgafos 168 (FF)®, BASF) and 2-(1 ,1- dimethylethyl)-6-methyl-4-[3-[[2,4,8,10-tetrakis(1 ,1-dimethylethyl)di- benzo[d,f][1 ,3,2]dioxaphosphepin-6-yl]oxy]propyl]phenol (e.g., Sumilizer GP®, Sumitomo Chemical) being most preferred.

In some embodiments, the polypropylene recycling material is extrusion-blended at least with 2-(1 ,1-dimethylethyl)-6-methyl-4-[3-[[2,4,8,10-tetrakis(1 ,1-dimethylethyl)di- benzo[d,f][1 ,3,2]dioxaphosphepin-6-yl]oxy]propyl]phenol (e.g., Sumilizer GP®, Sumitomo Chemical). In some embodiments, the polypropylene recycling material is extrusion-blended at least with tris(2,4-di-t-butylphenyl)phosphite (e.g., Irgafos 168 (FF)®, BASF). According to the present invention, the polypropylene recycling material is extrusion-blended, based on the total weight of the stabilized polypropylene recycled product, with from 0.02 to 0.28 wt.-%, preferably from 0.03 to 0.20 wt.-%, more preferably from 0.04 to 0.18 wt.-%, such as from 0.05 to 0.10 wt.-%, of the one or more secondary antioxidant(s).

The polypropylene recycling material is preferably extrusion-blended with one to three, more preferably with one or two and most preferably with one secondary antioxidant, wherein the secondary antioxidants are preferably selected from the compounds depicted above. c) Metal deactivators

Metal deactivators are mainly used in telecommunication insulation polymers to protect these polymers from copper ions. Without metal deactivators the long-term heat stability would be drastically reduced.

The effect of metal deactivators is to trap metals that may generate radicals. In particular, it is known for transition metals (e.g., Ti, Fe, Cu, Mn and Co) that they can easily change their oxidation state. In the presence of ions of such metals, the degradation of ROOH (hydroperoxides) can already occur at room temperatures, while respective degradation occurs at much higher temperatures (e.g., above 150 °C) in the absence thereof. A typical mechanism of hydroperoxide degradation is depicted in the following scheme:

ROOH + Me⁽ⁿ⁺¹⁾⁺ ROO* + Meⁿ⁺ + H⁺

ROOH + Meⁿ⁺ RO* + Me<ⁿ⁺¹>⁺ + OH’

2ROOH ROO* + RO* + H₂O

Scheme 3: Main mechanism of hydroperoxide degradation in the presence of metals.

Metal deactivators are usually chelating agents that form stable complexes with transition metals to prevent the reaction of transition metals with peroxides.

In contrast to primary antioxidants containing phenolic groups, which cannot form stable complexes with the transition metals, metal deactivators contain multiple atoms with lone pair of electrons (e.g., O, N, S and P) that could be given to the transition metal ion, thus forming covalent bonds. Thus, commonly used phenolic antioxidants, such as pentaerythrityl- tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate, do not form stable complexes with transition metals to prevent the reaction of transition metals with peroxides, and thus are not metal deactivators.

Metal deactivators can form complexes with transition metals comprising the range from hard cations (e.g., Ti⁴⁺ and Fe³⁺) to soft cations (e.g., Cu⁺). Metal deactivators usually act as chelating agents that form stable complexes, for example also with hard cations of the main group metals, such as Ca²⁺ and Al³⁺. It has been found that besides the transition metals, also metals of the main groups may facilitate degradation of polypropylene.

The one or more metal deactivator(s) is/are preferably selected from the group consisting of

N,N’-bis (3(3’,5’-di-tert-butyl-4’-hydroxyphenyl)propionyl)hydrazine, 2,2’-oxamido bis-(ethyl-3-

(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), N,N-bis(2-ethylhexyl)-4-methyl-1 H- benzotriazole-1-methanamine, N,N-bis(2-ethylhexyl)-5-methyl-1 H-benzotriazole-1- methanamine, and any combination thereof.

More preferably, the one or more metal deactivator(s) is/are phenolic chelating agent(s), preferably selected from the group consisting of N,N’-bis (3(3’,5’-di-tert-butyl-4’- hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF), 2,2’-oxamido bis-(ethyl- 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (e.g., Palmarole MDA. P. 11 G2®), and the combination thereof.

In particular embodiments, at least two metal deactivator(s) are used, wherein the metal deactivators mainly target at least two different metals or groups of metals. For example, the combination of N,N’-bis (3(3’,5’-di-tert-butyl-4’-hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF) and 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate) (e.g., Palmarole MDA. P. 11 G2®) has been found particularly suitable to target the metals of polypropylene recycling material and to efficiently stabilize this material.

According to the present invention, the polypropylene recycling material is extrusion-blended, based on the total weight of the stabilized polypropylene recycled product, with from 0.05 to

O.60 wt.-%, preferably from 0.08 to 0.40 wt.-%, more preferably from 0.10 to 0.25 wt.-%, such as from 0.12 to 0.18 wt.-% of the one or more metal deactivator(s).

The polypropylene recycling material is preferably extrusion-blended with one to four, more preferably with one to three and most preferably with one or two metal deactivators, wherein the metal deactivators are preferably selected from the compounds depicted above. In some embodiments, the polypropylene recycling material is extrusion-blended with one metal deactivator. In other embodiments, the polypropylene recycling material is extrusion-blended with two metal deactivators. Using two metal deactivators may allow targeting at least two different metals or groups of metals.

It has been surprisingly found that using metal deactivator(s), polypropylene recycling material can be sufficiently stabilized from degradation (particularly oxidative/heat degradation). In contrast to the stabilization of virgin polymers, the presence of metal deactivator(s) in polypropylene recycling material resulted in further stabilization from degradation. The use of metal deactivators even allowed a reduction of the content of the primary and secondary antioxidants, while obtaining an even better stabilizing effect.

In some embodiments, the polypropylene recycling material is extrusion-blended with less than 1 ,500 ppm (i.e., 0.15 wt.-%) of the sum of amounts of the one or more primary antioxidant(s) and the one or more secondary antioxidant(s), based on the total weight of the stabilized polypropylene recycled product.

According to the present invention, the polypropylene recycling material is extrusion-blended, based on the total weight of the stabilized polypropylene recycled product, with a) from 0.02 to 0.25 wt.-% of the one or more primary antioxidant(s), b) from 0.02 to 0.28 wt.-% of the one or more secondary antioxidant(s), c) from 0.05 to 0.60 wt.% of the one or more metal deactivator(s), and d) from 0.00 to 5.00 wt.-% of further additive(s) and/or carrier(s), e.g., from 0.01 to 0.05 wt.-% of one or more acid scavengers.

In some embodiments, the polypropylene recycling material can be extrusion-blended, based on the total weight of the stabilized polypropylene recycled product, with a) from 0.03 to 0.15 wt.-% of the one or more primary antioxidant(s), b) from 0.03 to 0.20 wt.-% of the one or more secondary antioxidant(s), c) from 0.08 to 0.40 wt.% of the one or more metal deactivator(s), and d) from 0.00 to 5.00 wt.-% of further additive(s) and/or carrier(s), e.g., from 0.01 to 0.05 wt.-% of one or more acid scavengers.

In some embodiments, the polypropylene recycling material can be extrusion-blended, based on the total weight of the stabilized polypropylene recycled product, with a) from 0.03 to 0.12 wt.-% of the one or more primary antioxidant(s), b) from 0.04 to 0.18 wt.-% of the one or more secondary antioxidant(s), c) from 0.10 to 0.25 wt.% of the one or more metal deactivator(s), and d) from 0.00 to 5.00 wt.-% of further additive(s) and/or carrier(s), e.g., from 0.01 to 0.05 wt.-% of one or more acid scavengers.

In some embodiments, the polypropylene recycling material can be extrusion-blended, based on the total weight of the stabilized polypropylene recycled product, with a) from 0.04 to 0.08 wt.-% of the one or more primary antioxidant(s), b) from 0.05 to 0.10 wt.-% of the one or more secondary antioxidant(s), c) from 0.12 to 0.18 wt.% of the one or more metal deactivator(s), and d) from 0.00 to 5.00 wt.-% of further additive(s) and/or carrier(s), e.g., from 0.01 to 0.05 wt.-% of one or more acid scavengers. The ranges suggested for addition of additives and additive carriers a) to d) have been empirically found based on the analysis of compounds present in the polypropylene recycling material to be stabilized and the stabilized polypropylene recycled product. Due to the change of composition during the lifetime of the material, i.e., including the preparation of the virgin polymer, the use of this polymer and the preparation of the recycled product, the contents of added additives have been selected in such a way that they can provide efficient stabilization. In this analysis the degradation of these additives as well as the presence of other compounds (e.g., other degradation products and metals) were considered.

In some embodiments, in the process according to the present invention, a polypropylene recycling material is extrusion-blended with a) one or more primary antioxidant(s), comprising at least one phenolic antioxidant, b) one or more secondary antioxidant(s), comprising at least one organic phosphorus antioxidant, c) one or more metal deactivator(s), comprising at least one, preferably at least two, phenolic chelating agent (s), and d) optionally further additive(s) and/or additive carrier(s).

In some embodiments, in the process according to the present invention, a polypropylene recycling material is extrusion-blended with a) one or more primary antioxidant(s), selected from the group consisting of pentaerythrityl- tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate (e.g., Irganox 1010®, BASF), 1 ,3, 5-tri-methyl-2 ,4,6-tris-(3, 5-di-tert. butyl-4-hydroxyphenyl)benzene (e.g., Irganox 1330 FF®, BASF), 2,5,7,8-tetramethyl-2(4’,8’,12’-trimethyltridecyl)chroman-6-ol (e.g., Irganox E201®, BASF) and any combination thereof, b) one or more secondary antioxidant(s), selected from the group of consisting of tris(2 ,4- di-tert-butylphenyl)phosphite (e.g., Irgafos 168 (FF)®, BASF), bis(2,4- dicumylphenyl)pentaerythritol diphosphite (e.g., Doverphos S-9228 CT®, Dover Chemical), 2-(1 ,1-dimethylethyl)-6-methyl-4-[3-[[2,4,8,10-tetrakis(1 ,1-dimethylethyl)di- benzo[d,f][1 ,3,2]dioxaphosphepin-6-yl]oxy]propyl]phenol (e.g., Sumilizer GP®, Sumitomo Chemical) and any combination thereof, c) one or more metal deactivator(s), selected from N,N’-bis (3(3’,5’-di-tert-butyl-4’- hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF), 2,2’-oxamido bis- (ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (e.g.,

Palmarole MDA. P. 11 G2®), and the combination thereof, preferably the combination thereof, and d) optionally further additive(s) and/or additive carrier(s). In a particularly preferred embodiment, in the process according to the present invention, a polypropylene recycling material is extrusion-blended with a) one or more primary antioxidant(s), comprising at least pentaerythrityl-tetrakis(3-(3’,5’- di-tert-butyl-4-hydroxyphenyl)propionate (e.g., Irganox 1010®, BASF), b) one or more secondary antioxidant(s), comprising at least tris(2,4-di-tert- butylphenyl)phosphite (e.g., Irgafos 168 (FF)®, BASF), c) one or more metal deactivator(s), comprising at least N,N’-bis (3(3’,5’-di-tert-butyl-4’- hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF) and 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (e.g.,

Palmarole MDA. P. 11 G2®), and d) optionally further additive(s) and/or additive carrier(s).

In a further particularly preferred embodiment, in the process according to the present invention, a polypropylene recycling material is extrusion-blended with a) pentaerythrityl-tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate (e.g.,

Irganox 1010®, BASF), b) tris(2,4-di-tert-butylphenyl)phosphite (e.g., Irgafos 168 (FF)®, BASF), c) N,N’-bis (3(3’,5’-di-tert. butyl-4’-hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF) and 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate) (e.g., Palmarole MDA. P. 11 G2®), and d) optionally further additive(s) and/or additive carrier(s).

In a still further particularly preferred embodiment, in the process according to the present invention, a polypropylene recycling material is extrusion-blended with a) one or more primary antioxidant(s), comprising at least pentaerythrityl-tetrakis(3-(3’,5’- di-tert-butyl-4-hydroxyphenyl)propionate (e.g., Irganox 1010®, BASF), b) one or more secondary antioxidant(s), comprising at least 2-(1 ,1-dimethylethyl)-6- methyl-4-[3-[[2,4,8,10-tetrakis(1 ,1-dimethylethyl)di-benzo[d,f][1 ,3,2]dioxaphosphepin-6- yl]oxy]propyl]phenol (e.g., Sumilizer GP®, Sumitomo Chemical), c) one or more metal deactivator(s), comprising at least N,N’-bis (3(3’,5’-di-tert-butyl-4’- hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF) and 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (e.g.,

In an also particularly preferred embodiment, in the process according to the present invention, a polypropylene recycling material is extrusion-blended with a) pentaerythrityl-tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate (e.g.,

Irganox 1010®, BASF), b) 2-(1 , 1 -dimethylethyl)-6-methyl-4-[3-[[2,4,8, 10-tetrakis(1 , 1 -dimethylethyl)di- benzo[d,f][1 ,3,2]dioxaphosphepin-6-yl]oxy]propyl]phenol (e.g., Sumilizer GP®, Sumitomo Chemical), c) N,N’-bis (3(3’,5’-di-tert-butyl-4’-hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF) and 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate) (e.g., Palmarole MDA. P. 11 G2®), and d) optionally further additive(s) and/or additive carrier(s). d) Further additives and additive carriers

In addition to the additives a) to c), further additives and carriers may be used in the process according to the present invention.

In particular, one or more acid scavenger(s) and/or one or more alkyl radical scavenger(s) may be further used in the process according to the present invention.

Accordingly, in some embodiments, in the process according to the present invention, a polypropylene recycling material is extrusion-blended with a) one or more primary antioxidant(s), b) one or more secondary antioxidant(s), c) one or more metal deactivator(s), and d) one or more acid scavenger(s) and/or one or more alkyl radical scavenger(s), and optionally further additive(s) and/or additive carrier(s).

In some embodiments, in the process according to the present invention, a polypropylene recycling material is extrusion-blended with at least a) one or more primary antioxidant(s), b) one or more secondary antioxidant(s), c) one or more metal deactivator(s), and d) one or more acid scavenger(s), and optionally one or more alkyl radical scavenger(s).

In these embodiments, the contents of additives may be used as defined above.

Acid scavengers

Acid scavengers are often used to protect the equipment against corrosion as well as to protect the polymer. In particular, hydrochloric acid generated from the chlorine content originating in polyolefins from catalyst residues may be neutralized by acid scavengers. It has been found that acid containing polymers may suffer from discoloration or deterioration during its use. Generally, acid scavengers can be divided into the three classes of compounds: metallic soaps, basic metal oxides and hydroxides and mineral agents. Generally, the one or more acid scavenger(s) can be selected from the group consisting of a metal oxide and a metal hydroxide such as CaO, MgO, AI2O3, ZnO, Mg(OH)2, Ca(OH)2, and a mineral agent such as hydrotalcite, e.g., Mg4,3Al2(OH)i2.3(CO3).mH2O, and any combination thereof.

Preferably, the one or more acid scavenger(s) is/are selected from metal oxides. Metal oxides are preferably used if adhesion issues are important (e.g., in some film applications) and the potential lubricating activity of other acid scavengers should be avoided.

In some preferred embodiments, the acid scavenger is MgO.

The polypropylene recycling material is preferably extrusion-blended, based on the total weight of the stabilized polypropylene recycled product, with from 0.01 to 0.05 wt.-%, more preferably from 0.01 to 0.04 wt.-%, such as from 0.01 to 0.02 wt.-% of the one or more acid scavenger(s).

The polypropylene recycling material is preferably extrusion-blended with one or two, preferably one acid scavenger, wherein the acid scavengers are preferably selected from the compounds depicted above.

In some embodiments, in the process according to the present invention, a polypropylene recycling material is extrusion-blended with at least a) pentaerythrityl-tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate (e.g.,

Irganox 1010®, BASF), b) tris(2,4-di-tert-butylphenyl)phosphite (e.g., Irgafos 168 (FF)®, BASF) and/or 2-(1 ,1- dimethylethyl)-6-methyl-4-[3-[[2,4,8,10-tetrakis(1 ,1-dimethylethyl)di- benzo[d,f][1 ,3,2]dioxaphosphepin-6-yl]oxy]propyl]phenol (e.g., Sumilizer GP®, Sumitomo Chemical), c) N,N’-bis (3(3’,5’-di-tert-butyl-4’-hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF) and 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate) (e.g., Palmarole MDA. P. 11 G2®), and d) MgO.

Alkyl radical scavengers

As described above, alkyl radical scavengers are the third class of antioxidants.

Preferably, the one or more alkyl radical scavenger(s) is/are selected from a lactone alkyl radical scavenger, hydroxylamine and the combination thereof.

More preferably, the one or more alkyl radical scavenger(s) are selected from the group consisting of [4-tert-butyl-2-(5-tert-butyl-2-oxo-3H-1-benzofuran-3-yl)phenyl]-3,5-di-tert-butyl- 4-hydroxybenzoate, hydroxylamine and the combination thereof. In particular hydroxylamine can react with radicals in non-stochiometric manner, thus only a small amount of this additive is needed to achieve excellent performance. Moreover, hydroxylamine is particularly suitable for polymer applications sensitive to discoloration as hydroxylamine does not contribute to color formation.

The polypropylene recycling material is preferably extrusion-blended, based on the total weight of the stabilized polypropylene recycled product, with from 0.002 to 0.02 wt.-%, more preferably from 0.003 to 0.01 wt.-%, such as from 0.004 to 0.008 wt.-% of the one or more alkyl radical scavenger(s).

The polypropylene recycling material is preferably extrusion-blended with one or two, preferably one alkyl radical scavenger, wherein the alkyl radical scavengers are preferably selected from the compounds depicted above.

Irganox 1010®, BASF), b) tris(2,4-di-tert-butylphenyl)phosphite (e.g., Irgafos 168 (FF)®, BASF) and/or 2-(1 ,1- dimethylethyl)-6-methyl-4-[3-[[2,4,8,10-tetrakis(1,1-dimethylethyl)di- benzo[d,f][1 ,3,2]dioxaphosphepin-6-yl]oxy]propyl]phenol (e.g., Sumilizer GP®, Sumitomo Chemical), c) N,N’-bis (3(3’,5’-di-tert-butyl-4’-hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF) and 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert. butyl-4- hydroxyphenyl)propionate) (e.g., Palmarole MDA. P. 11 G2®), d) MgO, and e) a lactone alkyl radical scavenger, such as [4-tert-butyl-2-(5-tert-butyl-2-oxo-3H-1- benzofuran-3-yl)phenyl]-3,5-di-tert-butyl-4-hydroxybenzoate or hydroxylamine.

Further additives

Still further additives may be used in the process according to the present invention. These additives may be further stabilizers (i.e. , compounds precluding degradation), modifiers (i.e. , compounds improving polymer performance and processing), fillers, flame retardants, compatibilizers, crosslinkers, colorants and others.

Examples of further suitable additives are UV-absorbers, e.g., HALS (Hindered amines light stabilizers) compounds.

Examples of modifying agents are antistatic - and anti-fogging agents, blowing agents, cling agents, lubricants & resins, nucleating agents and slip - and anti-blocking agents. Particularly preferred modifying agents for use for polypropylene recycled products in film application are lubricants, nucleating agents and slip - and anti-blocking agents.

The further additives can be selected from additives known in the art, and can preferably be selected from the group consisting of stabilizers, fillers, colorants, nucleating agents, antistatic agents, and mixtures thereof. Such additives are generally commercially available and are described, for example, in “Plastic Additives Handbook”, pages 871 to 873, 5^th edition, 2001 of Hans Zweifel.

Generally, the additives may be added to the polypropylene recycling material as single components, as compositions of some of these additives or as a composition of all additives (i.e., “onepack”), possibly further comprising a carrier (e.g., in the form of a masterbatch). In a onepack, one additive acts as a “carrier” for the respective other additives. The compositions are further described herein below.

Some of the additives falling into the definition of additives a) to d) may be regarded to belong to more than one of the described additive classes. In such a case, it is to be understood that for each of the additive classes a) to c) at least one compound must be added. For example, if one compound falls into the definition of a) and b), at least one additional compound must be added that falls into the definition of a) and/or b). In particular, if a metal deactivator c) can also function as a primary antioxidant a) (e.g., due to its phenolic groups), it is only considered a metal deactivator c), and a further compound must be added as the primary antioxidant a). Thus, at least one compound is used for each of the compounds a) to c).

Additive carriers

The polypropylene recycling material may be extrusion-blended in the presence of additive carriers. Additive carriers are generally known in the art.

Particularly preferred are polymeric carriers which are used to form a masterbatch. A masterbatch is a concentrated mixture obtained by the distribution of additives into a polymer carrier, preferably a polyolefin resin such as a polypropylene and/or polyethylene resin. Polyolefin resin can be semi-crystalline or can have cross-linkable silicon-containing groups, e.g., as described in EP 2657284 B1 and US 11 ,186,711 B2.

In some embodiments, the carrier comprises a C3-C5 alpha-olefin homo- or copolymer. In case, the carrier comprises a C3-C5 alpha-olefin copolymer, the comonomer content is preferably at least 2.0 wt.%, more preferably at least 5.0 wt.%, and preferably not more than 25 wt.-%, based on the total weight of the copolymer. The comonomer is preferably selected from C2-C8 alpha-olefins, more preferably from C2-C4 alpha-olefins and most preferably the comonomer is ethylene. Composition

The present invention also relates to a composition for stabilizing a polypropylene recycling material against degradation, preferably oxidative and/or thermal degradation, comprising, preferably consisting of: a) one or more primary antioxidant(s), b) one or more secondary antioxidant(s), c) one or more metal deactivator(s), and d) optionally further additive(s) and/or additive carrier(s).

The polypropylene recycling material intended for stabilization comprises, based on the total weight of the polypropylene recycling material, from 2 to less than 20,000 ppm of the sum of contents of the transition metals selected from titanium (Ti), zinc (Zn), copper (Cu) and iron (Fe), determined by X-ray fluorescence (XRF) spectroscopy as described herein.

In some embodiments, the composition comprises, preferably consists of a) one or more primary antioxidant(s), comprising at least one phenolic antioxidant, b) one or more secondary antioxidant(s), comprising at least one organic phosphorus antioxidant, c) one or more metal deactivator(s), comprising at least one, preferably at least two, phenolic chelating agent (s), and d) optionally further additive(s) and/or additive carrier(s).

The compounds a) to d) can generally by as defined above in the context of the process according to the present invention. A preferred further additive is one or more acid scavengers, such as a metal oxide, e.g., MgO.

In some embodiments, the composition comprises, preferably consists of a) one or more primary antioxidant(s), selected from the group consisting of pentaerythrityl- tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate (e.g., Irganox 1010®, BASF), 1 ,3,5-tri-methyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxyphenyl)benzene (e.g.,

Irganox 1330 FF®, BASF), 2,5,7,8-tetramethyl-2(4’,8’,12’-trimethyltridecyl)chroman-6-ol (e.g., Irganox E201®, BASF) and any combination thereof, b) one or more secondary antioxidant(s), selected from the group of consisting of tris(2 ,4- di-tert-butylphenyl)phosphite (e.g., Irgafos 168 (FF)®, BASF), bis(2,4- dicumylphenyl)pentaerythritol diphosphite (e.g., Doverphos S-9228 CT®, Dover Chemical), 2-(1 ,1-dimethylethyl)-6-methyl-4-[3-[[2,4,8,10-tetrakis(1 ,1-dimethylethyl)di- benzo[d,f][1 ,3,2]dioxaphosphepin-6-yl]oxy]propyl]phenol (e.g., Sumilizer GP®, Sumitomo Chemical) and any combination thereof, c) one or more metal deactivator(s), selected from N,N’-bis (3(3’,5’-di-tert-butyl-4’- hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF), 2,2’-oxamido bis- (ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (e.g.,

Palmarole MDA. P. 11 G2®), and the combination thereof, preferably the combination thereof, and d) optionally further additive(s) and/or additive carrier(s).

In a particularly preferred embodiment, the composition comprises, preferably consists of a) one or more primary antioxidant(s), comprising at least pentaerythrityl-tetrakis(3-(3’,5’- di-tert-butyl-4-hydroxyphenyl)propionate (e.g., Irganox 1010®, BASF), b) one or more secondary antioxidant(s), comprising at least tris(2,4-di-tert- butylphenyl)phosphite (e.g., Irgafos 168 (FF)®, BASF), c) one or more metal deactivator(s), comprising at least N,N’-bis (3(3’,5’-di-tert-butyl-4’- hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF) and 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (e.g.,

In a further particularly preferred embodiment, the composition comprises, preferably consists of a) pentaerythrityl-tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate (e.g.,

Irganox 1010®, BASF), b) tris(2,4-di-tert-butylphenyl)phosphite (e.g., Irgafos 168 (FF)®, BASF), c) N,N’-bis (3(3’,5’-di-tert-butyl-4’-hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF) and 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate) (e.g., Palmarole MDA. P. 11 G2®), and d) optionally further additive(s) and/or additive carrier(s).

In a still further particularly preferred embodiment, the composition comprises, preferably consists of a) one or more primary antioxidant(s), comprising at least pentaerythrityl-tetrakis(3-(3’,5’- di-tert-butyl-4-hydroxyphenyl)propionate (e.g., Irganox 1010®, BASF), b) one or more secondary antioxidant(s), comprising at least 2-(1 ,1-dimethylethyl)-6- methyl-4-[3-[[2,4,8,10-tetrakis(1 ,1-dimethylethyl)di-benzo[d,f][1 ,3,2]dioxaphosphepin-6- yl]oxy]propyl]phenol (e.g., Sumilizer GP®, Sumitomo Chemical), c) one or more metal deactivator(s), comprising at least N,N’-bis (3(3’,5’-di-tert-butyl-4’- hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF) and 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (e.g.,

Palmarole MDA. P. 11 G2®), and d) optionally further additive(s) and/or additive carrier(s), e.g., one or more acid scavengers such as MgO.

In an also particularly preferred embodiment, the composition comprises, preferably consists of a) pentaerythrityl-tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate (e.g.,

Irganox 1010®, BASF), b) 2-(1 ,1-dimethylethyl)-6-methyl-4-[3-[[2, 4,8,10-tetrakis(1 ,1 -dimethylethyl)di- benzo[d,f][1 ,3,2]dioxaphosphepin-6-yl]oxy]propyl]phenol (e.g., Sumilizer GP®, Sumitomo Chemical), c) N,N’-bis (3(3’,5’-di-tert-butyl-4’-hydroxyphenyl)propionyl)hydrazine (e.g., Irganox MD 1024®, BASF) and 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate) (e.g., Palmarole MDA. P. 11 G2®), and d) optionally further additive(s) and/or additive carrier(s), e.g., one or more acid scavengers such as MgO.

In any of the above embodiments, the composition may further comprise one or more acid scavenger(s), and optionally one or more alkyl radical scavenger(s), wherein these compounds are preferably as described above in the context of the process. Further additives and additive carriers may be present in the composition as also described above.

Preferably, the composition comprises, based on the total weight of the composition: a) from 4.0 to 40.0 wt.-% of the one or more primary antioxidant(s), b) from 6.5 to 80.0 wt.-% of the one or more secondary antioxidant(s), c) from 13.5 to 75.0 wt.-% of the one or more metal deactivator(s), and d1) from 0.0 to 75.0 wt.-% of further additive(s), e.g., from 1.0 to 40.0 wt.-% of one or more acid scavengers, wherein the components a) to d1) add up to 100%.

In some embodiments, the composition comprises, based on the total weight of the composition: a) from 10.0 to 30.0 wt.-% of the one or more primary antioxidant(s), b) from 15.0 to 60.0 wt.-% of the one or more secondary antioxidant(s), c) from 20.0 to 65.0 wt.-% of the one or more metal deactivator(s), and d1) from 0.0 to 65.0 wt.-% of further additive(s) e.g., from 1.0 to 30.0 wt.-% of one or more acid scavengers, wherein the components a) to d1) add up to 100%.

In some embodiments, the composition comprises, based on the total weight of the composition: a) from 15.0 to 20.0 wt.-% of the one or more primary antioxidant(s), b) from 20.0 to 40.0 wt.-% of the one or more secondary antioxidant(s), c) from 30.0 to 60.0 wt.-% of the one or more metal deactivator(s), and d1) from 0.0 to 60.0 wt.-% of further additive(s) e.g., from 1.0 to 20.0 wt.-% of one or more acid scavengers, wherein the components a) to d1) add up to 100%.

In some embodiments, the composition comprises, based on the total weight of the composition: a) from 15.0 to 20.0 wt.-% of the one or more primary antioxidant(s), b) from 20.0 to 40.0 wt.-% of the one or more secondary antioxidant(s), c) from 30.0 to 60.0 wt.-% of the one or more metal deactivator(s), and d1) from 0.0 to 10.0 wt.-% of further additive(s) e.g., from 1.0 to 10.0 wt.-% of one or more acid scavengers, wherein the components a) to d1) add up to 100%.

The composition may be combined with an additive carrier preferably selected from the carriers described above. Most preferably, the additive carrier is a polyolefin resulting in a masterbatch composition.

Preferably, the composition (1) is combined with an additive carrier in a weight ratio of composition to additive carrier of from 5 : 95 to 70 : 30. Accordingly, the additive carrier may be present in the final composition in 30 to 95 wt.-%, based on the total weight of the so formed composition (2) comprising the additive carrier.

In some embodiments, the composition (2) comprises, based on the total weight of the composition: a) from 0.2 to 20.0 wt.-% of the one or more primary antioxidant(s), b) from 0.3 to 30.0 wt.-% of one or more secondary antioxidant(s), c) from 0.5 to 45.0 wt.-% of one or more metal deactivator(s), d1) from 0.0 to 10.0 wt.-% of further additive(s), e.g., from 0.1 to 10.0 wt.-% of one or more acid scavengers, and d2) from 30.0 to 95.0 wt.-% of additive carrier(s), wherein the components a) to d2) add up to 100%.

In some embodiments, the composition (2) comprises, based on the total weight of the composition: a) from 0.3 to 15.0 wt.-% of the one or more primary antioxidant(s), b) from 0.4 to 25.0 wt.-% of one or more secondary antioxidant(s), c) from 0.8 to 40.0 wt.-% of one or more metal deactivator(s), d1) from 0.0 to 5.0 wt.-% of further additive(s), e.g., from 0.1 to 5.0 wt.-% of one or more acid scavengers, and d2) from 30.0 to 95.0 wt.-% of additive carrier(s), wherein the components a) to d2) add up to 100%.

Product

The present invention is further directed to a stabilized polypropylene recycled product obtainable by the process according to any of the above-described embodiments.

The stabilized polypropylene recycled product is stabilized against degradation, preferably oxidative and/or thermal degradation. Accordingly, the degradation of the stabilized polypropylene recycled product is decelerated and/or minimized. This can be seen in the change of the oxidation induction time (OIT) at 200 °C and enhanced oxidation induction temperature, as well as on the presence of other degradation products (e.g., acetic acid etc.) and/or volatile compounds, as shown in the examples herein below.

Use

Further, the present invention also relates to the use of the composition according to any one of the above-described embodiments for stabilizing a polypropylene recycling material against degradation, preferably oxidative and/or thermal degradation.

Experimental Section

Measurement methods

The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples, unless otherwise defined. a) Melt flow rate

Melt flow rates were measured with a load of 2.16 kg (MFR₂) at 230 °C as indicated. The melt flow rate is that quantity of polymer in grams which the test apparatus standardized to ISO 1133 extrudes within 10 minutes at a temperature of 230 °C under a load of 2.16 kg. b) Determination of components of a polymer material

1. Fourier-transform infrared (FTIR) spectroscopy

Sample preparation:

All calibration samples and samples to be analyzed were prepared in similar way, on molten pressed plates. About 2 to 3 g of compounds to be analyzed were melted at 190°C. Subsequently, for 20 seconds, 60 to 80 bar pressure was applied in a hydraulic heating press. Next, the samples were cooled to room temperature in 40 seconds in a cold press under the same pressure, in order to control the morphology of the compound. The thickness of the plates was controlled by metallic calibrated frame plates 2.5 cm by 2.5 cm, 100 to 200 pm thick (depending MFR from the sample); two plates were produced in parallel at the same time and in the same conditions. The thickness of each plate was measured before any FTIR measurements were performed; all plates were between 100 to 200 pm thick.

To control the plate surface and to avoid any interference during the measurement, all plates were pressed between two double-sided silicone release papers.

In case of powder samples or heterogeneous compounds, the pressing process was repeated three times to increase homogeneity by pressing and cutting the sample in the same conditions as described before.

Spectrometer:

Standard transmission FTIR spectroscope such as Bruker Vertex 70 FTIR spectrometer was used with the following set-up: o a spectral range of 4000-400 cm'¹, o an aperture of 6 mm, o a spectral resolution of 2 cm'¹, o with 16 background scans, 16 spectrum scans, o an interferogram zero filling factor of 32 o Norton Beer strong anodization.

Spectra were recorded and analyzed in Bruker Opus software.

Calibration samples:

As FTIR is a secondary method, several calibration standards were compounded to cover the targeted analysis range, typically from: o 0.2 wt.-% to 2.5 wt.-% for PA o 0.1 wt.-% to 5 wt.-% for PS o 0.2 wt.-% to 2.5 wt.-% for PET o 0.1 wt.-% to 4 wt.-% for PVC

The following commercial materials were used for the compounds: Borealis HC600TF as iPP, Borealis FB3450 as HDPE and for the targeted polymers such RAMAPET N1S (Indorama Polymer) for PET, Ultramid® B36LN (BASF) for Polyamide 6, Styrolution PS 486N (Ineos) for High Impact Polystyrene (HIPS), and for PVC Inovyn PVC 263B (under powder form).

All compounds were made at small scale in a Haake kneader at a temperature below 265°C and less than 10 minutes to avoid degradation.

Additional antioxidant such as Irgafos 168 (3000 ppm) was added to minimize the degradation.

Calibration:

The FTIR calibration principle was the same for all the components: the intensity of a specific FTI R band divided by the plate thickness is correlated to the amount of component determined by ¹H or ¹³C solution state NMR on the same plate.

Each specific FTIR absorption band was chosen due to its intensity increase with the amount of the component concentration and due to its isolation from the rest of the peaks, whatever the composition of the calibration standard and real samples.

This methodology is described in the publication from Signoret and al. “Alterations of plastic spectra in MIR and the potential impacts on identification towards recycling”, Resources, conservation and Recycling journal, 2020, volume 161 , article 104980.

The wavelength for each calibration band was: o 3300 cm'¹ for PA, o 1601 cm'¹ for PS, o 1410 cm'¹ for PET, o 615 cm-¹ for PVC, o 1167 cm'¹ for iPP.

For each polymer component i, a linear calibration (based on linearity of Beer-Lambert law) was constructed. A typical linear correlation used for such calibrations is given below: where xi is the fraction amount of the polymer component i (in wt.-%),

Ei is the absorbance intensity of the specific band related to the polymer component i (in a.u. absorbance unit, values see above), d is the thickness of the sample plate,

Ai and Bi are two coefficients of correlation determined for each calibration curve. No specific isolated band can be found for C2-rich fraction and as a consequence the C2-rich fraction is estimated indirectly,

^XC2 rich ⁼ 100 — (x_ipp + X_PA + X_ps + X_PET + X_EVA + X_pvc + X_cflalk + _ta(c)

The Chalk and Talc contents are estimated “semi-quantitatively”. Hence, this renders the C2 rich content “semi-quantitative”.

For each calibration standard, wherever available, the amount of each component was determined by either ¹H or ¹³C solution state NMR, as primary method (except for PA). The NMR measurements were performed on the exact same FTIR plates used for the construction of the FTIR calibration curves.

2. X-ray fluorescence (XRF) for the content of inorganic elements

The content of inorganic elements was determined by X-ray fluorescence (XRF). The instrument used for the XRF measurements was a wavelength dispersive Zetium (2,4kW) from Malvern Panalytical. The instrument was calibrated with Adpol, RoHs, Toxel standards from Malvern Panalytical and from a custom set of calibration standards (referred to in the following as “Custom”) also from Malvern Panalytical according to the following table:

The analyses are done under vacuum on a plaque with a diameter of 40mm and a thickness of 2mm.

The method is generally used to determine the quantitative content of Na, Mg, Al, Si, P, S, Ca, Ti, Zn, Cu, Br, Cl, K, Sr, Fe in polyolefin matrix within defined ranges of these standards.

The content of each precise element was evaluated with the following standards:

Elements which are not covered by standards, or in case the content is outside of the calibrated standard range, are then analyzed with a semi-quantitative mode (software Omnian from Malvern Panalytical). For elements not covered by the calibration standards, no value is reported if the corresponding peak is not visible and therefore cannot be analyzed with the software Omnian.

The CH content needed to run the semiquantitative evaluation with Omnian was estimated by the software itself.

3. Static headspace analysis for the screening of marker substances

The parameters of the applied headspace gas chromatography mass spectrometry (HS/GC/MS) method are described here.

For the measurement of a standard solution containing 0.8 pg/pL acetic acid (target concentration in 2-butanol) 5 pL of the standard were injected into a 20mL headspace vial and tightly closed with a PTFE cap.

After production, the pellet samples were air-tightly stored and kept until analysis. The samples were analysed by HS/GC/MS in order to determine acetic acid as the relevant marker substance. Therefore, about 10 g of the polymer sample were cryo-milled with the aid of liquid nitrogen and a rotor mill (ring sieve, aperture size: 1 mm). Directly after milling an aliquot of 2.000 ± 0.100 g of the cryo-milled portion was weighed in a 20 ml HS vial and tightly sealed with a PTFE cap. The samples were analysed by HS/GC/MS at 100 °C / 2 h isothermal headspace conditions.

Applied HS parameters for the analyses of standards and samples differed in the vial equilibration time and the HS oven temperature. Apart from that, method parameters were kept the same for standard and sample runs. The mass spectrometer was operated in scan mode and a total ion chromatogram (TIC) was recorded for each analysis. Identification of substances was supported by deconvolution and a retention time comparison to the respective marker substance in the standard. More detailed information on method parameters is given below:

• HS parameters (Agilent G1888 Headspace Sampler)

Vial equilibration time: 5 min (standard), 120 min (sample)

Oven temperature: 200 °C (standard), 100 °C (sample)

Loop temperature: 205 °C

T ransfer line temperature: 210 °C

Low shaking

• GC parameters (Agilent 7890A GC System)

Column: ZB-WAX 7HG-G007-22 (30 m x 250 pm x 1 pm)

Carrier gas: Helium 5.0

Flow: 2 ml/min

Split: 10:1

GC oven program: 35 °C for 0.1 min

10 °C/min until 250 °C

250 °C for 1 min

• MS parameters (Agilent 5975C inert XL MSD)

Acquisition mode: Scan

Scan parameters:

Low mass: 20

High mass: 200

Threshold: 10

For further data evaluation extracted ion chromatograms (EICs) of the measured marker compound in the standard and in the samples were used. The corresponing target ion of the marker substance acetic acid was m/z 60.

The standard concentration of a marker substance in the HS vial (Cc^tandard) was calculated according equation 1 , where the marker substance concentration in the liquid standard ^_cstandard^ _{was mu}|tipii_ed by the injection volume (y^ⁿJ^ectlon ) _Of the standard and divided by the volume of the HS vial (V_C ^HS). Here, a HS volume of 20 ml is used by default. Equation 1 For each marker compound in the standard a response factor (Rf ) was calculated according equation 2. Equation 2

Therein, the marker compound concentration is divided by the integrated peak area of the corresponding marker compound in the EIC (Peak area^standard).

In order to estimate the respective marker compound concentration in the headspace of a sample (Cg^ample), equation 3, was used. Therefore, the obtained response factor from equation 2 is multiplied by the peak area of the corresponding marker compound in the EIC of the sample run (Peak area^Sample). Equation 3

4. TD GC-FID for the screening of low-boiling substances (LBS) and high-boiling substances (HBS)

This method describes the semi-quantitative determination of organic compounds emitting from polyolefins. It is similar to the VDA 278 (October 2011) but includes specific adjustments.

After production, the pellet samples were air-tightly stored and kept until analysis. An aliquot of 60 ± 5 mg was prepared from the stored sample. Trimming the aliquot aimed for a maximum coherent area. It was not the aim to create the largest possible surface area by cutting the aliquot into smaller pieces. The diameter of the sample injection tube was used first. Length and thickness were chosen accordingly, considering the specified aliquot weight. The aliquot was directly desorbed using heat and a flow of helium gas. Volatile and semi-volatile organic compounds were extracted into the gas stream and cryo-focused prior to the injection into a gas chromatographic (GC) system for analysis. The method comprised two extraction stages: In the analysis of low-boiling substances (LBS) the aliquot was desorbed at 90 °C for 30 min to determine volatile organic compounds in the boiling I elution range up to n-C25 (n- pentacosane). The analysis of high-boiling substances (HBS) involved a further desorption step of the same aliquot at 120 °C for 60 min to determine semi-volatile compounds in the boiling I elution range from n-C14 (n-tetradecane) to n-C32 (n-dotriacontane).

Similar to the VOC and FOG value in the VDA 278, the LBS is calculated as toluene equivalent (TE) and the HBS is calculated as hexadecane equivalent (HE) applying a semi-quantitation and a respective calibration. The result is expressed in “pg/g”. Integration parameters for the LBS and HBS evaluation were chosen in such way that the „area reject" corresponds to the area of 1 pg/g (TE and HE, respectively). Thus, smaller peaks did not add to the semi-quantitative result. The GC oven program was kept the same, no matter if a calibration run, an LBS run or an HBS run had been performed. It started at 50 °C (1 min hold), followed by a ramp of 10 °C/min and an end temperature of 320 °C (10 min hold). For the GC column an Agilent DB5: 50 m x 250 pm x 0.25 pm (or comparable) was used. The method requires a Thermal Desorption System TDS 3 (Gerstel) and a Cooled Injection System CIS 4 (Gerstel) as well as a GC system with a flame ionization detector (FID) but does not involve a mass spectrometer. Instead of 280 °C the CIS end temperature was always set to 380 °C.

5. Gas Chromatography (GC)

Other additives (using respective calibration standards) were determined by gas chromatography (GC). Therefore, about 10 g of the polymer sample were cryo-milled with the aid of liquid nitrogen and a rotor mill (ring sieve, aperture size: 1 mm). After that, a portion of approximately 0.5 g of the milled sample was extracted with a mixture of Pyridine/Toluene (7/3 = v/v). This extraction solvent solution also contained 2 mL acetic acid per litre solvent mixture. Extraction was performed at 100 °C for 60 min under constant stirring. After that, the suspension was allowed to cool down to room temperature. Subsequently, the suspension was filtrated and divided into two separate portions. 0.1 mL of N-Methyl-N-trimethylsilyl- trifluoroacetamide (MSTFA, CAS no. 24589-78-4) were added to one of the extract portions for derivatisation and kept at 100 °C for 20 min. The other extract portion was not derivatised. Both solutions were tested by GC using a flame ionisation detector (FID) and a DB-1 type column. Helium was used as carrier gas. “Stearate” content was determined as the sum of myristic acid (CAS-no. 544-63-8), palmitic acid (CAS-no. 57-10-3), stearic acid (CAS-no. 57- 11-4) and arachidic acid (506-30-9). Sumilizer GP refers to (6-3-(3-tert-butyl-4-hydroxy-5- methylphenyl) propoxy)-2,4,8,10-tetra-tert. butyldibenz (d,t)(1.3.2) dioxaphosphepin) (CAS- no. 203255-81-6).

6. High Performance Liquid Chromatography (HPLC)

Antioxidant content was determined via high performance liquid chromatography (HPLC) after extraction with ethyl acetate. Therefore, about 10 g of the polymer sample were cryo-milled with the aid of liquid nitrogen and a rotor mill (ring sieve, aperture size: 1 mm). After that, a portion of approximately 0.5 g of the milled sample was extracted using ethyl acetate as a solvent. Extraction was performed at 95 °C for 90 min under constant stirring. After letting the mixture cool down to room temperature again it was filtrated and put to the HPLC test for the quantification of antioxidants. The HPLC system was equipped with a C18 column for the separation and a diode array detector (DAD) for detection. The detection wavelength was set to 276 nm and the quantitation was performed with respective calibration standards for N,N’- bis(3(3’,5’-di-tert-butyl-4’-hydroxyphenyl)propionyl)hydrazine (CAS no. 32687-78-8), Pentaerythrityl-tetrakis(3-(3’,5’-di-tert.-butyl-4-hydroxyphenyl)-propionate (CAS no. 6683-19- 8), Tris(2,4-di-tert-butylphenyl)phosphite (CAS no. 31570-04-4) and Tris (2,4-di-tert- butylphenyl)phosphate (CAS no. 95906-11-9). Further HPLC parameters are listed below: c) Oxidation induction (01) time and oxidation induction temperature measurement

The oxidation induction time (01 time) at 200 °C was determined with a TA Instrument Q20 according to ISO11357-6. Calibration of the instrument was performed with indium (In), zinc (Zn), and tin (Sn). Each polymer sample (cylindrical geometry with a diameter of 4 mm and thickness of 650pm±100pm) was placed in an open aluminum crucible, heated from 20 °C to 200 °C at a rate of 20 °C min^-1 in nitrogen (>99.95 vol.% N2) with a gas flow rate of 50 mL min^-1 , and allowed to rest for 5 min before the atmosphere was switched to pure oxygen (>99.95 vol.% O2), also at a flow rate of 50 mL min^-1. The samples were maintained at constant temperature, and the exothermal heat associated with oxidation was recorded. The oxidation induction time was the time interval between the initiation of oxygen flow and the onset of the oxidative reaction. Each presented data point was the average of two independent measurements.

The oxidation induction temperature was determined with a TA Instrument Q20 according to ISO11357-6. Calibration of the instrument was performed with indium (In), zinc (Zn), and tin (Sn). Each polymer sample (cylindrical geometry with a diameter of 4 mm and thickness of 650pm±100pm) was placed in an open aluminum crucible, immediately heated to 350 °C with a gas flow rate of 50 mL min^-1 under pure oxygen (>99.95 vol.% O2). The exothermal heat associated with oxidation was recorded. The oxidation induction temperature is the onset of the oxidative reaction. The oxidation induction temperature was evaluated according to ISO11357-6. d) Crystex analysis, crystalline fraction (CF) and soluble fraction (SF)

The crystalline (CF) and soluble fractions (SF) of the PCR polypropylene resins as well as the ethylene contents and intrinsic viscosities of the respective fractions were analyzed by use of the CRYSTEX instrument, Polymer Char (Valencia, Spain) in line with ISO16152-2022 - Method 2. Details of the technique and the method can be found in literature (Ljiljana Jeremie, Andreas Albrecht, Martina Sandholzer & Markus Gahleitner (2020) Rapid characterization of high-impact ethylene-propylene copolymer composition by crystallization extraction separation: comparability to standard separation methods, International Journal of Polymer Analysis and Characterization, 25:8, 581-596).

The crystalline and amorphous fractions are separated through temperature cycles of dissolution at 160 °C, crystallization at 40 °C and re-dissolution in 1 ,2,4-trichlorobenzene at 160 °C. Quantification of SF and CF and determination of ethylene content (C2) are achieved by means of an integrated infrared detector (IR4) and for the determination of the intrinsic viscosity (IV) an online 2-capillary viscometer is used.

The IR4 detector is a multiple wavelength detector measuring IR absorbance at two different bands (CH3 stretching vibration (centered at app. 2960 cm'¹) and the CH stretching vibration (2700-3000 cm'¹) that are serving for the determination of the concentration and the ethylene content in ethylene-propylene copolymers. The IR4 detector is calibrated with series of 8 EP copolymers with known ethylene content in the range of 2 wt.-% to 69 wt.-% (determined by ¹³C-NMR) and each at various concentrations, in the range of 2 and 13 mg/ml. To encounter for both features, concentration and ethylene content at the same time for various polymer concentrations expected during Crystex analyses the following calibration equations were applied:

Cone = a + b*Abs(CH) + c*(Abs(CH))² + d*Abs(CH₃) + e*(Abs(CH₃)² + f*Abs(CH)*Abs(CH₃) (Equation 4)

CH₃/1000C = a + b*Abs(CH) + c* Abs(CH₃) + d * (Abs(CH₃)/Abs(CH)) + e * (Abs(CH₃)/Abs(CH))² (Equation 5)

The constants a to e for equation 4 and a to f for equation 5 were determined by using least square regression analysis.

The CH₃/1000C is converted to the ethylene content in wt.-% using following relationship:

Wt.-% (ethylene in EP copolymers) = 100 - CH₃/1000TC * 0.3 Intrinsic viscosity (IV) of the PCR polypropylene resin and its soluble and crystalline fractions are determined with a use of an online 2-capillary viscometer and are correlated to corresponding I ’s determined by standard method in decalin according to ISO 1628-3. Calibration is achieved with various EP PP copolymers with IV = 2-4 dL/g. The determined calibration curve is linear:

IV (dL/g) = a* Vsp/c

The samples to be analyzed are weighed out in concentrations of 10 mg/ml to 20 mg/ml. To avoid injecting possible gels and/or polymers which do not dissolve in TCB at 160 °C, like PET and PA, the weighed out sample was packed into a stainless steel mesh MW 0, 077/D 0.05 mm.

After automated filling of the vial with 1 ,2,4-TCB containing 250 mg/l 2,6-tert-butyl-4- methylphenol (BHT) as antioxidant, the sample is dissolved at 160 °C until complete dissolution is achieved, usually for 60 min, with constant stirring of 400 rpm. To avoid sample degradation, the polymer solution is blanketed with the N2 atmosphere during dissolution.

A defined volume of the sample solution is injected into the column filled with inert support where the crystallization of the sample and separation of the soluble fraction from the crystalline part is taking place. This process is repeated two times. During the first injection the whole sample is measured at high temperature, determining the IV [dl/g] and the C2 [wt.- %] of the PP composition. During the second injection the soluble fraction (at low temperature) and the crystalline fraction (at high temperature) with the crystallization cycle are measured (wt.-% SF, wt.-% CF, wt.-% C2, wt.-% C2(SF), wt.-% C2(CF), IV(SF), IV(CF)), where the wt.- % CF is calculated in the following way: wt.-% CF = 100 - wt.-% SF.

Examples

Materials used in the examples

1. Preparation of the polypropylene recycling material

For Comparative Examples CE1-3 and CE5 and Inventive Examples IE1-7, IE10-11 and IE15- 16, a Swedish post consumer plastic trash was used that was enriched in post consumer flexible polypropylene article having flexible polymer articles in a content of 89 wt.-% (with a PP:PE ratio of 40.8:1).

For Examples IE5’, IE8, and CE4, a polypropylene fraction from a German post-consumer plastic trash fulfilling the specification DSD323-2 was used as the precursor mixed-plastic recycling stream. The content of flexible polymer articles was 71.1 wt.-% (with a PP:PE ratio of 0.3:1).

For Inventive Example IE9, a German post-consumer plastic trash was used that was enriched in post-consumer flexible polypropylene articles having a content of flexible polymer articles of 81.4 wt.-% (with a PP:PE ratio of 23.8:1).

For Comparative Examples CE6-8 and Inventive Examples IE12-14, the feedstock comprised labels obtained as a by-product from container recycling, such as PET bottles.

The process was conducted by the sequence of steps: a) providing the polyolefin recycling streams described above; b) separating via sieving; c) removing metal particles; d) sorting according to polymer type, transparency, coIor and reflectance via optical sorters; e) selecting the polypropylene transparent (only Comparative Example CE4 and Inventive Examples IE8 and IE9) or colored (all other examples) fraction; f) size-reducing via wet grinding; g) washing by cold alkaline wash, hot alkaline wash and rinsing (sub-steps g1a) to g3)); h) mechanical drying followed by thermal drying; i) separating via air sifter and selecting the flexible flake fraction. Examples CE6-8 and IE12-14 originated from labels. Thus, as this feedstock was already pre-sorted and relatively homogeneous, no sorting step was required.

For CE4, IE5’, IE8, IE9, IE13 and IE14, the pellettisation and additivation was done according to the conditions identified in Table 1 by using the flakes.

Table 1 : Extrusion conditions.

For CE1-3 and CE5-8 and IE1-7, IE10-12 and IE15-16, small-scale samples were prepared (“pre-compacting”) and the pelletisation and additivation of the flexible flakes was executed in two steps. In a first processing step, the flakes were compacted and pelletized through a milder extrusion on a standard co-rotating twin-screw extruder ZK50 by Collin Lab & Pilot Solutions GmbH in the absence of additives. The extruder had a diameter of 50 mm, a length to diameter ratio (L/D) of 22 and a diameter ratio (Do/Di) of 1.25. The polymer flakes were dosed into the main hopper of the extruder. The extruder barrel temperatures were set to 20/190/250/220/205/230/220/185/200°C. The screw speed was 80 rpm and the throughput rate was about 10 kg/h. A strand pelletizer with 2 holes having 3 mm in diameter was used to pelletize the polymer. In this way the polypropylene recycling material was prepared for a subsequent blend-extrusion with the additives. The contents and properties of the polypropylene recycling material are depicted in Tables 4A to 4E below, e.g., in Comparative Examples CE1 and CE5-7 no additives were added. CE1 , CE5 and CE6 were not extruded a second time. Due to the use of different sorting and/or batches of post-consumer plastic waste as well as to the variation in the small-scale pre-compacted samples, the contents and properties may vary between the examples.

2. Additives

The additives used are depicted in Table 2 below:

Table 2: Additives.

Extrusion-blending of the polypropylene recycling material with additives

In a second processing step, the pelletized flakes and additives (as listed in Table 3 below) were compounded on a standard co-rotating twin-screw extruder Prism TSE 24 by Thermo Fisher Scientific. The extruder had a diameter of 23.6 mm, a length to diameter ratio (L/D) of 40 and a diameter ratio (Do/Di) of 1.77. The extruder barrel temperatures were set to

20/170/210/220/230/230/220/210/200/200/200°C. The screw speed was 450 rpm and throughput rate was 8 kg/h. The polymers and additives were dosed from separate scales into the main hopper of the extruder. Strand pelletizer with 3 holes having 3 mm diameter was used to pelletize the product. For the addition of the additives masterbatches MB1 to MB12 were prepared, as depicted in Table 2 below. MB1 and MB2 correspond to a basic stabilizer for virgin polymers, which were used in the comparative examples and were mixed with further additives to prepare the inventive examples. For MB8 and MB9, the secondary antioxidant 1 was replaced by either a mixture of secondary antioxidant 1 and hydroxylamine (FS301) or by secondary antioxidant 2, respectively. Table 3: Additive addition (in ppm).

Results

The recycled products obtained were measured for their contents and properties and the results are depicted in Tables 4A to 4E below.

Table 4A: Results.

Table 4B: Results (continued). Table 4C: Results (continued).

Table 4D: Results (continued).

Table 4E: Results (continued). nm = not measured * MD2 was added intentionally in a 1 :1 ratio with MD1 to the same base recycling polymer. A qualitative check of the chromatogram confirms a detector response at the expected retention time for MD2, on similar scale of magnitude for MD2 as for MD1.

** intentionally added amount (Table 2). These values were not quantitatively measured.

*** “SA1-ox” denotes the oxidated (inactive) form of SA1. **** FOG and VOC indicate low- and high-boiling substances (LBS and HBS), as described in the measurement methods.

^#The amount of additives added in Example CE4 was 1650 ppm of PrA and 1650 ppm of SA1.

LOD = limit of detection; LOQ = limit of quantification

The differences between added additives and measured additives mostly result from the initial contents of these additives in the polymer and the use (reaction) of the additives during the recycling process. However, as is found in the examples, the contents of additives used were sufficient for efficient stabilization. The same source of waste starting material was used for Examples CE1-3, CE5 and IE1-7, IE10-11 and IE15-16. For Comparative Examples CE1-3 and for Inventive Examples IE1-IE7, the same batch was used (with CE1 as the starting material for all of these Examples), and for Comparative Example CE5 and Inventive Examples IE10-11 and IE14-15 another same batch was used. For the Comparative Examples CE1-3, Inventive Examples IE1-IE7, and IE5’, the colored fraction was selected. For examples IE8 and IE9, and CE4, the transparent fraction of the sorting process was selected. For Comparative Examples CE6-8 and Inventive Examples IE12-14, the feedstock comprised labels obtained from containers such as PET bottles. Examples CE6-8 and I E12 were prepared from the same batch (with CE6 as the as the starting material for all of these Examples). All samples of the lEs could be sufficiently stabilized.

Further, polymer samples not sorted by color/transparency were analyzed for their contents without additivation (not shown). The values obtained were between those of the transparent fraction and the colored fraction. Accordingly, similar stabilization results are expected for the non-sorted polymer fractions.

For Inventive Examples IE5’, IE8, and IE9, the OIT temperature was measured on the washed flakes, before extrusions. For all three examples, the OIT temperature was 199°C. The improved stabilization in the Inventive Examples over to the Comparative Examples (without additivation - CE1 , or in the presence of a basis stabilization and in the absence of a metal deactivator - CE2-CE4) can be seen in the enhanced OIT temperature. For Inventive Examples IE8 and IE9, the oxidation induction time at 200°C also increased. Further, the degradation products are mostly reduced as depicted by the usually lower contents of volatile organic compounds (VOC) and semi-volatile organic compounds (FOG), as well as of acetic acid.

When comparing examples IE3 and IE4, it can be seen that upon increasing the metal deactivator content, the content of the basis stabilization (only primary and secondary antioxidants) can be reduced for very similar stabilization results.

The stabilization results do not strongly vary based on the kind of the secondary antioxidant used (examples IE2/IE3 vs. IE7).

The stabilization effect was independent on the waste samples used (presorted vs. nonpresorted trash; examples IE8 vs. IE9).

Further, the melt flow rate was lower in the Inventive Examples vs. the Comparative Examples (comparing IE8 and IE9 vs. CE4; or IE12-14 vs. CE6-8). Thus, rheological properties could also be improved by the suggested additivation. This also indicates the improved stabilization of the Inventive Examples. Examples CE6-8 and IE12-14 were carried out with a different kind of waste material and they show similar improvements. Notably, there are huge differences between CE6 and CE1/CE5 in the OIT temperature and MFR. Still, the suggested additivation is advantageous for different kinds of polypropylene waste materials. As depicted in Inventive Examples IE10 vs. IE11 , the content of acetic acid can be reduced by the addition of MgO as acid scavenger, by maintaining the high OIT temperature - even at reduced content of metal deactivator. Inventive Examples IE15 and IE16 show that stabilization is reached by the use of only one kind of metal deactivator compound. The recycled products obtained were also measured for their properties via the Crystex method and the results are depicted in Table 5 below.

Table 5: Results Crystex method.

Claims

1. A process for stabilizing a polypropylene recycling material against degradation, preferably oxidative and/or thermal degradation, comprising extrusion-blending a polypropylene recycling material with a) from 0.02 to 0.25 wt.-% of one or more primary antioxidant(s), b) from 0.02 to 0.28 wt.-% of one or more secondary antioxidant(s), c) from 0.05 to 0.60 wt.% of one or more metal deactivator(s), and d) from 0.00 to 5.00 wt.-% of further additive(s) and/or additive carrier(s), to form a stabilized polypropylene recycled product, wherein the polypropylene recycling material comprises, based on the total weight of the polypropylene recycling material, from 2 to less than 20,000 ppm of the sum of contents of the transition metals selected from titanium (Ti), zinc (Zn), copper (Cu) and iron (Fe), determined by X-ray fluorescence (XRF) spectroscopy as described in the specification.

2. The process according to claim 1 , wherein the further additives comprise one or more acid scavenger(s) and/or one or more alkyl radical scavenger(s).

3. The process according to any one of the preceding claims, wherein a) the one or more primary antioxidant(s) comprise(s) a phenolic antioxidant, b) the one or more secondary antioxidant(s) comprise(s) an organic phosphorus antioxidant, and c) the one or more metal deactivator(s) comprise(s) a phenolic chelating agent, preferably at least two phenolic chelating agents.

4. The process according to any one of the claims 2 or 3, wherein the one or more acid scavenger(s) comprise(s) a metal oxide, and the one or more alkyl radical scavenger(s) comprise(s) a lactone alkyl radical scavenger and/or hydroxylamine.

5. The process according to any one of the preceding claims, wherein a) the one or more primary antioxidant(s) is/are selected from the group consisting of 2,6-di-tert. butyl-4-methyl phenol, pentaerythrityl-tetrakis(3-(3’,5’-di-tert-butyl-4- hydroxyphenyl)propionate, octadecyl 3-(3’,5’-di-tert-butyl-4- hydroxyphenyl)propionate, 1 ,3,5-tri-methyl-2,4,6-tris-(3,5-di-tert-butyl-4- hydroxyphenyl)benzene, 2,2’-thiodiethylenebis-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate, calcium (3,5-di-tert-butyl-4-hydroxy benzyl monoethyl- phosphonate), 1 ,3,5-tris(3’,5’-di-tert-butyl-4’-hydroxybenzyl)-isocyanurate, bis- (3,3-bis-(4’-hydroxy-3’-tert-butylphenyl)butyric acid)glycolester, 4,4’-thiobis(2-tert- butyl-5-methylphenol), 2,5,7,8-tetramethyl-2(4’,8’,12’-trimethyltridecyl)chroman-6- ol, 1 ,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1 ,3,5-triazine-2,4,6- (1 H,3H,5H)-trione, 4,6-bis (octylthiomethyl)-o-cresol, butylated reaction product of p-cresol and dicyclopentadiene, and any combination thereof; b) the one or more secondary antioxidant(s) is/are selected from the group consisting of tris(2,4-di-tert-butylphenyl)phosphite, tetrakis-(2,4-di-tert-butylphenyl)-4,4’- biphenylen-di-phosphonite, di-stearyl-pentaerythrityl-di-phosphite, bis(2,4- dicumylphenyl)pentaerythritol diphosphite, 2-(1 ,1-dimethylethyl)-6-methyl-4-[3- [[2,4,8,10-tetrakis(1 ,1-dimethylethyl)di-benzo[d,f][1 ,3,2]dioxaphosphepin-6- yl]oxy]propyl]phenol, di-stearyl-thio-di-propionate, di-lauryl-thio-di-propionate, di- octadecyl-disulfide, and any combination thereof; and c) the one or more metal deactivator(s) is/are selected from the group consisting of N,N’-bis (3(3’,5’-di-tert-butyl-4’-hydroxyphenyl)propionyl)hydrazine, 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), N,N-bis(2-ethylhexyl)- 4-methyl-1 H-benzotriazole-1-methanamine, N,N-bis(2-ethylhexyl)-5-methyl-1 H- benzotriazole-1-methanamine, and any combination thereof.

6. The process according to any one of claims 2 to 5, wherein d) the one or more acid scavenger(s) is/are selected from the group consisting of a metal oxide and a metal hydroxide such as CaO, MgO, AI2O3, ZnO, Mg(OH)2, Ca(OH)2, and a mineral agent such as hydrotalcite, e.g.,

Mg4,3Al2(OH)i2.3(CC>3).mH2O, and any combination thereof; and/or e) the one or more alkyl radical scavenger(s) is/are selected from the group consisting of [4-tert-butyl-2-(5-tert. butyl-2-oxo-3H-1-benzofuran-3-yl)phenyl]-3,5- di-tert-butyl-4-hydroxybenzoate, hydroxylamine and the combination thereof.

7. The process according to any one of the preceding claims, wherein the polypropylene recycling material is extrusion-blended with at least a) pentaerythrityl-tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate, b) tris (2,4-di-tert-butylphenyl) phosphite or 2-(1 ,1-dimethylethyl)-6-methyl-4-[3- [[2,4,8,10-tetrakis(1 ,1-dimethylethyl)di-benzo[d,f][1 ,3,2]dioxaphosphepin-6- yl]oxy]propyl]phenol, c1) N,N’-bis (3(3’,5’-di-tert-butyl-4’-hydroxyphenyl)propionyl)hydrazine, c2) 2,2’-oxamido bis-(ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), and d) optionally MgO.

8. The process according to any one of the preceding claims, wherein the polypropylene recycling material is extrusion-blended with less than 1 ,500 ppm of the sum of amounts of the one or more primary antioxidant(s) and the one or more secondary antioxidant(s), based on the total weight of the stabilized polypropylene recycled product.

9. The process according to any one of the preceding claims, wherein the polypropylene recycling material is extrusion-blended, based on the total weight of the stabilized polypropylene recycled product, with a) from 0.03 to 0.15 wt.-% of the one or more primary antioxidant(s), b) from 0.03 to 0.20 wt.-% of the one or more secondary antioxidant(s), c) from 0.08 to 0.40 wt.% of the one or more metal deactivator(s), and d) from 0.00 to 5.00 wt.-% of further additive(s) and/or carrier(s).

10. The process according to any one of the preceding claims, wherein the polypropylene recycling material comprises, based on the total weight of the polypropylene recycling material, at least one, preferably all, of i) to iv): i) from 100 to less than 30,000 ppm of calcium (Ca), determined by X-ray fluorescence (XRF) spectroscopy as described in the specification, ii) from 10 to less than 1 ,000 ppm of aluminum (Al), determined by X-ray fluorescence (XRF) spectroscopy as described in the specification, iii) from 0 to less than 2.5 wt.-% of the sum of amounts of PA, PET and PS, determined by FTIR as described in the specification, and iv) from 1 to 15 wt.-% of ethylene units (C2), determined by Fourier-transform infrared (FTIR) spectroscopy as described in the specification.

11. The process according to any one of the preceding claims, the process comprising the following steps: a) providing a precursor polyolefin recycling material stream (A) that contains polypropylene recycling material, preferably flexible polypropylene recycling material; b) sieving the precursor polyolefin recycling stream (A) to create a sieved polyolefin recycling stream (B) having only articles with a longest dimension in the range from 30 to 400 mm; c) removing metal articles from the sieved polyolefin recycling material stream (B) to obtain a purer polyolefin recycling stream (C); d) sorting the polyolefin recycling material stream (C) by means of one or more optical sorters at least by polymer type, transparency and color, and optionally reflectance, and selecting the polypropylene colored or polypropylene transparent fraction, thereby generating a sorted polypropylene recycling material stream (D); e) reducing the size of the sorted polypropylene recycling stream (D) to form a flaked polypropylene recycling material stream (E); f) washing the flaked polypropylene recycling material stream (E) in an alkaline solution at a temperature in the range of from 20 to 95 °C to obtain a washed polypropylene recycling material stream (F); g) drying the washed polypropylene recycling stream (F) to obtain a dried polypropylene recycling material stream (G); h) optionally conducting further recycling steps to obtain a further processed polypropylene recycling material stream (H); i) extrusion-blending the polypropylene recycling material stream (G) or (H) with one or more primary antioxidant(s), one or more secondary antioxidant(s), one or more metal deactivator(s), and optionally further additives and/or additive carriers, to form a stabilized polypropylene recycled product (I); j) preferably pelletizing, the stabilized polypropylene recycled product (I) to form a pelletized stabilized polypropylene recycled product (J); and k) optionally aerating the stabilized polypropylene recycled product (I) or (J) to remove volatile organic compounds, thereby generating an aerated, preferably pelletized, stabilized polypropylene recycled product (K).

12. A composition for stabilizing a polypropylene recycling material against degradation, preferably oxidative and/or thermal degradation, comprising, preferably consisting of: a) one or more primary antioxidant(s), b) one or more secondary antioxidant(s), c) one or more metal deactivator(s), and d) optionally further additive(s) and/or additive carrier(s), preferably, wherein the compounds a) to d) are as defined in any one of claims 2 to 7, wherein the polypropylene recycling material comprises, based on the total weight of the polypropylene recycling material, from 2 to less than 20,000 ppm of the sum of contents of the transition metals selected from titanium (Ti), zinc (Zn), copper (Cu) and iron (Fe), determined by X-ray fluorescence (XRF) spectroscopy as described in the specification.

13. The composition according to claim 12, wherein the composition comprises, based on the total weight of the composition: a) from 4.0 to 40.0 wt.-% of the one or more primary antioxidant(s), b) from 6.5 to 80.0 wt.-% of the one or more secondary antioxidant(s), c) from 13.5 to 75.0 wt.-% of the one or more metal deactivator(s), and d1) from 0.0 to 75.0 wt.-% of further additive(s), wherein the components a) to d1) add up to 100%, and wherein the composition is optionally combined with an additive carrier in a weight ratio of composition to additive carrier of from 5 : 95 to 70 : 30.

14. A stabilized polypropylene recycled product obtainable by the process according to any one of claims 1 to 11.

15. Use of the composition according to any one of claims 12 and 13 for stabilizing a polypropylene recycling material against degradation, preferably oxidative and/or thermal degradation, wherein the polypropylene recycling material comprises, based on the total weight of the polypropylene recycling material, from 2 to less than 20,000 ppm of the sum of contents of the transition metals selected from titanium (Ti), zinc (Zn), copper (Cu) and iron (Fe), determined by X-ray fluorescence (XRF) spectroscopy as described in the specification.